The Li3 2xMgxV2（PO4）3/C （x-=0, 0.01, 0.03 and 0.05） composites were prepared by a sol-gel method and characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical measurements. The XRD results reveal that a small amount of Mg2＋ doping into Li sites does not significantly change the monoclinic structure of Li3V2（PO4）3, but Mg-doped Li3W2（PO4）3 has larger cell volume than the pristine Li3V2（PO4）3. All Mg-doped composites display better electrochemical performance than the pristine one, and Liz.94Mgo.03Vz（P04）3/C composite exhibits the highest capacity and the best cycle performance among all above-mentioned composites. The analysis of Li＋ diffusion coefficients in Li3V2（PO4）3/C and Li2.94Mgo.03V2（P04）3/C indicates that rapid Li＋ diffusion results from the doping of Mg2＋ and the rapid Li＋ diffusion is responsible for the better electrochemical performance of Mg-doped Li3V2（PO4）3/C composite cathode materials.
